Resin Molding Apparatus and Resin Molding Method

ABSTRACT

Disclosed is a resin molding apparatus capable of enhancing transfer accuracy, reducing the cost of a molding apparatus, and shortening a molding cycle. The resin molding apparatus includes a first mold; a second mold disposed in opposition to the first mold; a transfer plate ( 34 ) attached to one of the first and second molds and comprising a transfer surface bearing a pattern of pits and projections and oriented toward a cavity (C 1 , C 2 ); and a thermal insulation layer ( 40 ) disposed between the transfer plate ( 34 ) and the one of the first and second molds and formed through growth from the transfer plate ( 34 ) side or from the one of the first and second mold sides. Being disposed between the transfer plate ( 34 ) and the one of the first and second molds, the thermal insulation layer ( 40 ) can restrain dissipation of thermal energy of a molding material toward the mold. This can restrain formation of a skin layer, which would otherwise result from a sharp drop in temperature of the molding material, whereby transfer accuracy can be enhanced.

TECHNICAL FIELD

The present invention relates to a resin molding apparatus and a resinmolding method.

BACKGROUND ART

Conventionally, in a molding machine; for example, an injection moldingmachine, resin is melted within a heating cylinder through applicationof heat; the thus-molten resin is charged into a cavity of a moldingapparatus; and the resin within the cavity is cooled to set, therebyyielding a molded article.

The injection molding machine has a molding apparatus, which serves as aresin molding apparatus; a mold-clamping apparatus; and an injectionapparatus. The injection apparatus includes a heating cylinder formelting resin through application of heat; an injection nozzle attachedto the front end of the heating cylinder and adapted to inject themolten resin; and a screw disposed within the heating cylinder rotatablyand in a manner capable of advancing and retreating. The moldingapparatus includes a stationary mold and a movable mold. Themold-clamping apparatus advances and retreats the movable mold, wherebythe molding apparatus performs mold closing, mold clamping, and moldopening. When mold clamping is performed, a cavity is formed between thestationary mold and the movable mold.

In a metering step, when the screw is rotated, the resin fed into theheating cylinder is melted and stored ahead of the screw. In the courseof this operation, the screw is retreated. In this period, the moldingapparatus performs mold closing and mold clamping. Subsequently, in aninjection step, the screw is advanced, whereby the resin stored ahead ofthe screw is ejected from the injection nozzle and is charged into thecavity. Next, in a cooling step, the resin within the cavity is cooledto set. Subsequently, mold opening is performed, and the molded articleis ejected.

FIG. 1 is a sectional view of a conventional molding apparatus.

In FIG. 1, reference numeral 11 denotes a molding apparatus for moldingan article, such as a light guide plate; reference numeral 12 denotes astationary mold; and reference numeral 13 denotes a movable molddisposed in a manner capable of advancing and retreating in relation tothe stationary mold 12. By means of an unillustrated mold-clampingapparatus, the movable mold 13 is advanced; i.e., mold closing isperformed; the movable mold 13 is brought into contact with thestationary mold 12; i.e., mold clamping is performed, thereby formingcavities C1, C2, each having a rectangular shape, between the stationarymold 12 and the movable mold 13; and the movable mold 13 is retreatedfrom the stationary mold 12; i.e., mold opening is performed.

Reference numeral 15 denotes a sprue formed in the stationary mold 12.Communication is established between the tip end of the sprue 15 and thecavities C1, C2 through gates g1, g2, respectively.

The movable mold 13 includes an upper plate 21 and a lower plate 22,which supports the upper plate 21. A transfer plate 34 is attached to asurface of the movable mold 13 which is located within the cavities C1,C2 and faces the stationary mold 12. The transfer plate 34 has atransfer surface which faces the stationary mold 12 and on which finepits and projections are formed in a predetermined pattern.Temperature-regulating channels 23 are formed in the lower plate 22. Atemperature-regulating medium is run through the temperature-regulatingchannels 23 so as cool the molding apparatus 11 and resin within thecavities C1, C2.

An unillustrated injection apparatus is disposed in a manner capable ofadvancing and retreating in relation to the molding apparatus 11. Aninjection nozzle of the injection apparatus is pressed against thestationary mold 12 of the molding apparatus 11 in a mold-clamped state,and resin is ejected from the injection nozzle. The ejected resin ischarged into the cavities C1, C2 through the gates g1, g2, respectively.

The resin in the cavities C1, C2 is cooled, by thetemperature-regulating medium, to set. At this time, the pattern of thetransfer surface of the transfer plate 34 is transferred onto the resin.Subsequently, mold opening is performed, thereby yielding a light guideplate (refer to, for example, Patent Document 1).

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No.2000-249538

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the case where very fine pits and projections are formed onthe transfer surface, the conventional molding apparatus 11 may fail totransfer the pattern with a sufficient accuracy, resulting in lowtransfer accuracy.

A conceivable cause for the above-mentioned problem is as follows: inthe case of use of the molding apparatus 11 whose temperature becomeslower than a glass transition temperature of resin, when a molten resinflows into the cavities C1, C2 and comes into contact with wall surfacesof the cavities C1, C2, the molten resin is cooled instantaneously; as aresult, a solidified layer; i.e., a skin layer, is formed on the surfaceof the resin.

The state of formation of the skin layer varies depending on moldingconditions for a light guide plate, the type of resin, etc. Generally,time of formation; i.e., time of growth, is said to be on the order of0.1 second or less, and the thickness of the skin layer is said to beabout tens of micrometers. When resin comes into contact with the wallsurfaces of the cavities C1, C2, formation of the skin layer hinders theresin from flexibly following the profiles of the wall surfaces in thecourse of charge of the resin into the cavities C1, C2, resulting inoccurrence of a molding defect, such as a weld, defective transfer, orthe like. In the case where very fine pits and projections are formed onthe transfer surface as mentioned above, the pattern fails to betransferred onto the resin with a sufficient accuracy, resulting in lowtransfer accuracy.

According to a conceivable measure to cope with the above-mentionedproblem, in order to finish transfer before formation of the skin layer,the temperature of the molding apparatus 11 is raised for increasingfluidity of resin. However, increasing the temperature of the moldingapparatus 11 elongates time required for cooling resin to acorresponding extent, thereby elongating a molding cycle. According toanother conceivable measure, a temperature-regulating mechanism isdisposed within the molding apparatus 11 for regulating the temperatureof the molding apparatus 11. However, this not only increases the costof the molding apparatus 11 but also consumes a large amount of energyfor regulating the temperature of the molding apparatus 11, resulting inan increase in the cost of a light guide plate.

Further, according to a conceivable method for enhancing transferaccuracy, the pressure within the cavities C1, C2 is increased so as tomechanically crush the skin layer for establishing plastic deformation.However, this not only increases the size of the mold-clamping apparatusbut also deteriorates the pattern on the transfer plate 34, therebyimpairing the durability of the transfer plate 34.

An object of the present invention is to solve the above-mentionedproblems in the conventional molding apparatus 11 and to provide a resinmolding apparatus and a resin molding method which can enhance transferaccuracy, reduce the cost of a molding apparatus, and shorten a moldingcycle.

Means for Solving the Problems

To achieve the above-mentioned object, a resin molding apparatus of thepresent invention comprises a first mold; a second mold disposed inopposition to the first mold; a transfer plate attached to one of thefirst and second molds and comprising a transfer surface bearing apattern of pits and projections and oriented toward a cavity; and athermal insulation layer disposed between the transfer plate and the oneof the first and second molds and formed through growth from thetransfer plate side or from the one of the first and second mold sides.

EFFECTS OF THE INVENTION

According to the present invention, the resin molding apparatuscomprises a first mold; a second mold disposed in opposition to thefirst mold; a transfer plate attached to one of the first and secondmolds and comprising a transfer surface bearing a pattern of pits andprojections and oriented toward a cavity; and a thermal insulation layerdisposed between the transfer plate and the one of the first and secondmolds and formed through growth from the transfer plate side or from theone of the first and second mold sides.

In this case, being disposed between the transfer plate and the one ofthe first and second molds, the thermal insulation layer can restrainconduction of thermal energy of a molding material toward the mold. Thiscan restrain formation of a skin layer, which would otherwise resultfrom a sharp drop in temperature of the molding material. As a result,transfer accuracy can be enhanced.

Since a mold-clamping force for plastically deforming the skin layer canbe reduced, not only can the size of an injection molding machine bereduced, but also the durability of the transfer plate can be enhanced.

Since the temperature of the resin molding apparatus can be set low toan extent corresponding to the enhancement of transfer accuracy, thetransfer plate and the one of the first and second molds can lowertemperature more quickly. Therefore, a molding cycle can be sufficientlyshortened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a conventional thermally insulatedmold.

FIG. 2 is a pair of sectional views showing a resin molding method in afirst embodiment of the present invention.

FIG. 3 is a perspective view showing a main portion of a thermalinsulation layer in the first embodiment of the present invention.

FIG. 4 is an enlarged view showing the main portion of the thermalinsulation layer in the first embodiment of the present invention.

FIG. 5 is a series of views showing a first method for forming ahoneycomb structure in the first embodiment of the present invention.

FIG. 6 is a series of views showing a second method for forming ahoneycomb structure in the first embodiment of the present invention.

FIG. 7 is a graph showing characteristics of a molding apparatus in thefirst embodiment of the present invention.

FIG. 8 is a pair of sectional views showing a resin molding method in asecond embodiment of the present invention.

FIG. 9 is a graph showing characteristics of a molding apparatus in thesecond embodiment of the present invention.

FIG. 10 is a first view showing a method for forming a thermalinsulation layer in a third embodiment of the present invention.

FIG. 11 is a second view showing the method for forming a thermalinsulation layer in the third embodiment of the present invention.

FIG. 12 is a pair of views showing a method for forming a thermalinsulation layer in a fourth embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   20, 61: molding apparatus-   24A: stationary mold-   24B: movable mold-   34: transfer plate-   40: thermal insulation layer-   C, C1, C2: cavity

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will next be described in detailwith reference to the drawings. In this case, an injection moldingmachine, which serves as a molding machine, and a molding apparatus,which serves as a resin molding apparatus, will be described.

FIG. 2 is a pair of sectional views showing a resin molding method in afirst embodiment of the present invention, wherein (a) is a view showinga state in which a resin 30, which serves as a molding material, ischarged into cavities C1, C2, and (b) is a view showing a state in whichmold clamping has been performed.

In FIG. 2, reference numeral 61 denotes a molding apparatus, whichserves as a resin molding apparatus for molding an article, such as alight guide plate; reference numeral 24A denotes a stationary mold,which serves as a first mold member and as a first mold; and referencenumeral 24B denotes a movable mold, which serves as a second mold memberand as a second mold, disposed in a manner capable of advancing andretreating in relation to the stationary mold 24A. By means of anunillustrated mold-clamping apparatus, the movable mold 24B is advanced;i.e., mold closing is performed; the movable mold 24B is brought intocontact with the stationary mold 24A; i.e., mold clamping is performed,thereby forming cavities C1, C2, each having a rectangular shape,between the stationary mold 24A and the movable mold 24B; and themovable mold 24B is retreated from the stationary mold 24A; i.e., moldopening is performed.

Reference numeral 15 denotes a sprue formed in the stationary mold 24A.Communication is established between the tip end of the sprue 15 and thecavities C1, C2 through gates g1, g2, respectively.

The movable mold 24B includes an upper plate 21 and a lower plate(backing plate) 22, which supports the upper plate 21. A thermalinsulation layer 40 is formed on a surface of the movable mold 24B whichis located within the cavities C1, C2 and faces the stationary mold 24A.A transfer plate 34 is attached to a surface of the thermal insulationlayer 40 which faces the stationary mold 24A. The transfer plate 34 hasa transfer surface which faces the stationary mold 24A and on which finepits and projections are formed in a predetermined pattern.

Temperature-regulating channels 23 are formed in the lower plate 22. Atemperature-regulating medium; for example, water, is run through thetemperature-regulating channels 23 so as to cool the molding apparatus61 and resin 30 within the cavities C1, C2. Temperature-regulatingchannels similar to the temperature-regulating channels 23 can also beformed in the stationary mold 24A for running water therethrough.

An unillustrated injection apparatus is disposed in a manner capable ofadvancing and retreating in relation to the molding apparatus 61. Aninjection nozzle of the injection apparatus is pressed against thestationary mold 24A of the molding apparatus 61 in a mold-clamped state,and the resin 30 is ejected from the injection nozzle. The ejected resin30 is charged into the cavities C1, C2 through the gates g1, g2,respectively.

The resin 30 in the cavities C1, C2 is cooled, by the above-mentionedwater, to set. At this time, the pattern on the transfer surface of thetransfer plate 34 is transferred onto the resin 30. Subsequently, moldopening is performed, thereby yielding a light guide plate.

The present embodiment uses the stationary mold 24A as the first mold,and the movable mold 24B as the second mold. While the movable mold isdisposed above the stationary mold, the movable mold can be advanced andretreated by a press mechanism. In this case, the stationary mold isused as a stationary lower mold, and the movable mold is used as amovable upper mold.

In the present embodiment, the temperature of the above-mentioned wateris regulated such that the temperature of the molding apparatus 61 asmeasured when molding is started is set a predetermined value;specifically, about 40° C., lower than the temperature of theconventional molding apparatus 11.

For establishing the above-mentioned temperature condition, the thermalinsulation layer 40 is formed on the movable mold 24B as mentionedpreviously.

FIG. 3 is a perspective view showing a main portion of the thermalinsulation layer in the first embodiment of the present invention. FIG.4 is an enlarged view showing the main portion of the thermal insulationlayer in the first embodiment of the present invention.

The thermal insulation layer 40 has a honeycomb structure whose cellseach have the shape of a regular polygon; in the present embodiment, aregular hexagon, in section.

Meanwhile, in the case where a polymeric material, for example, isdisposed between the transfer plate 34 and the upper plate 21 for use asa thermal insulation layer, in the course of actual molding,contractions associated with heat cycles cause the thermal insulationlayer to rub against the surface of the transfer plate 34; consequently,the transfer plate 34 wears. In the case of molding of light guideplates mentioned previously, the molding apparatus 61 is required tohave a durability of 1,000,000 or more shots. The thermal conductivityof a polymeric material is about two orders of magnitude lower than thatof a steel material used to form the molding apparatus 61. Therefore, apolymeric material is an optimum material for the thermal insulationlayer in terms of thermal conductivity, but remains an unsatisfactorymaterial for the thermal insulation layer in terms of durability.

According to another conceivable method, the thermal insulation layer isformed from a ceramic material, such as zirconia, by a film formationprocess. Since zirconia has a coefficient of linear expansion close tothat of a steel material, use of zirconia is less likely to raise theproblem of rubbing caused by contractions associated with heat cycles,as compared with the case of use of the polymeric material. However,since the thermal insulation performance of zirconia is low, in order toexhibit the thermal insulation effect intended by the present invention,the thermal insulation layer of zirconia may need to have a thickness ofabout 100 μm to about 1 mm. In this case, even when the thermalinsulation layer can be actually formed, the formed thermal insulationlayer is of a highly fragile structure. Therefore, contractionsassociated with heat cycles and the application of a large injectionforce, a mold-clamping force, or the like cause cracking of the thermalinsulation layer. As a result, the durability of the thermal insulationlayer drops.

Thus, in the present embodiment, the thermal insulation layer 40 isformed into a honeycomb structure whose cells each have the shape of aregular hexagon in section as mentioned previously.

Meanwhile, in the case of molding of an optical medium, such as a lightguide plate, for example, a pressure of up to about 300 kg/cm² may beapplied to a circular region having a diameter of 12 cm. The transferplate 34 to be used in molding is usually formed by nickelelectroforming. The present embodiment also uses the transfer plate 34formed by nickel electroforming. The transfer plate 34 has a thicknessof about 0.3 mm. A pattern of fine pits and projections each having asubmicron size is formed on the surface of the transfer plate 34.

The transfer plate 34 is attached to the surface of the upper plate 21mechanically or by air chuck. In order to mitigate rubbing caused bycontractions associated with heat cycles, the surface of the upper plate21 is coated with a highly wear-resistant material, such as DLC (DiamondLike Carbon); thus, a DLC film is formed. In this case, since polishingthe surface of the film is impossible, the surface of the film has acertain roughness. Also, voids each having a diameter of tens ofmicrometers to 100 micrometers may be generated.

In order to avoid transfer of the shapes of voids onto the surface of alight guide plate through the thin transfer plate 34 with a resultantformation of associated marks on the surface of the light guide plate,the aforementioned honeycomb structure is employed. The honeycomb pitchP of the honeycomb structure is 0.1 μm to 100 μm inclusive, preferably 1μm to 10 μm inclusive. This range is determined in consideration of thedisposition of the thermal insulation layer 40 between the movable mold24B and the transfer plate 34. Generally, the honeycomb pitch P is setfar smaller than that of a honeycomb structure formed within the moldingapparatus 11 for the purpose of thermal insulation.

Metal is used to form the honeycomb structure of the thermal insulationlayer 40. The thickness of a wall of the honeycomb structure; i.e., awall thickness D, is set to 0.01 μm to 10 μm inclusive, preferably 0.1μm to 5 μm inclusive. This range is determined for the following reason:assuming that, for example, void portions 42 of the honeycomb structureare filled with air, whose thermal conductivity is negligibly low ascompared with that of a steel material, in order for the thermalinsulation layer 40 to exhibit about one-tenth the thermal conductivityof a steel material, the percentage of the void portions 42; i.e.,porosity, must be 90%. A honeycomb height H indicative of the height(formation height) of the honeycomb structure is set to 10 μm to 10 mminclusive.

Assuming that, the honeycomb pitch P is, for example, 10 μm, the wallthickness D of the honeycomb structure is on the order of 1 μm or less.In forming a microhoneycomb structure having, for example, a wallthickness D of 1 μm, a honeycomb pitch P of 10 μm, and a honeycombheight H of 1 mm over a large area of ten-odd cm, use of a fabricationmethod based on so-called LIGA (Lithographie, Galvanoformung, Abformung)process is preferred, since such a method is superior in forming astructure whose ratio of height to area is high; i.e., a“high-aspect-ratio structure.” Since the LIGA process itself is wellknown, detailed description thereof is omitted. Briefly, the LIGAprocess is carried out as follows: an X-ray-sensitive resist material isapplied, in the form of a thick film, onto a substrate; the film isexposed to synchrotron radiation (SR) (X-ray exposure) via an X-ray maskwhich uses Au, Be, or the like as an absorber; and exposed portions ormasked portions of the film are developed and removed, thereby yieldinga resist microstructure.

The resist microstructure is subjected to electroforming, therebyforming a replica. A honeycomb structure can be formed by injectionmolding or the like using the replica.

In the case where an LIGA process is employed, conceivable embodimentsare as follows: an embodiment in which a honeycomb structure is formedon a surface of the transfer plate 34 which faces the movable mold 24B,and an embodiment in which a honeycomb structure is formed on a surfaceof the movable mold 24B which faces the transfer plate 34.

Next, a method for forming a honeycomb structure will be described.

FIG. 5 is a series of views showing a first method for forming ahoneycomb structure in the first embodiment of the present invention.FIG. 6 is a series of views showing a second method for forming ahoneycomb structure in the first embodiment of the present invention.

A honeycomb structure is formed on the surface of the transfer plate 34which faces the movable mold 24B as follows. As shown in FIG. 5, whilethe transfer plate 34 (made of nickel) is used as a substrate, anX-ray-sensitive resist material 44 is applied, in the form of a thickfilm, onto the back surface (a surface which faces the movable mold 24B)of the transfer plate 34 (alternatively, a film of the resist material44 is affixed). The thickness of the resist material 44 is adjusted to apredetermined value by polishing or the like. The resist material 44 isexposed to synchrotron radiation (SR) via an X-ray mask 46, and thendevelopment is carried out, thereby yielding a negative honeycombstructure 48 having a structure width of 1 μm corresponding to the wallthickness D, and a repetition cycle of 10 μm corresponding to thehoneycomb pitch P (FIGS. 5(A), 5(B)). Subsequently, nickelelectroforming is carried out to grow a honeycomb structure (FIG. 5(C)).At this time, the transfer surface (the lower surface in FIG. 5) of thetransfer plate 34 is protected with an appropriate material, such asresist. After nickel electroforming, the honeycomb height is adjusted bypolishing or the like, thereby yielding the thermal insulation layer 40joined to the transfer plate 34 (FIG. 5(D)).

Usually, the thickness of the resist material 44 to be irradiated by asingle X-ray exposure is on the order of hundreds of micrometers.Therefore, when a far thicker thermal insulation layer 40 is to beformed, another honeycomb structure must be additionally formed on thepreviously formed honeycomb structure. This can be carried out by, forexample, a multiple-exposure LIGA process. Specifically, as shown inFIG. 6, after completion of the first exposure, development is notcarried out immediately, but the second layer of a resist material 50may be formed on the first layer of the resist material 44. Since thehoneycomb structure of the first layer eliminates the risk of transferof a honeycomb pattern (a pattern of honeycomb structure) onto a lightguide plate through the transfer plate 34, the honeycomb pitch P of thehoneycomb structure of the second layer can be rendered greater thanthat (e.g., 10 μm) of the honeycomb structure of the first layer. When arequired thickness of a microstructure of the resist material isobtained through repetition of similar exposure, development isperformed collectively. In this manner, a negative honeycomb structure52 of multiple honeycombs can be formed. The negative honeycombstructure 52 is subjected to nickel electroforming. Finally, the resistlayers 44, 50 are removed, thereby yielding the thermal insulation layer40 having a nickel honeycomb structure of a required thickness.

Meanwhile, in the case of forming a honeycomb structure on the surfaceof the movable mold 24B which faces the transfer plate 34, basically,the same method as that employed for forming a honeycomb structure bynickel electroforming described above can be used. However, since asteel material cannot be grown by electroforming, preferably, ametal-powder forming technique is used in place of electroforming, suchas nickel electroforming. In this case, a procedure up to the step offorming the negative honeycomb structures 48, 52 remains the same. Thesubsequent step uses a metal-powder sinter forming technique in place ofelectroforming. In this case, a metal powder of the same material (steelmaterial) as that of the molding apparatus 61 is used for restraininggeneration of thermal stress between the thermal insulation layer 40 andthe movable mold 24B, which could otherwise result from a difference inthermal expansion coefficient.

At the time of sintering, volume contracts by several percent to 10-oddpercent, depending on the composition. Thus, sintering is performed soas to form a mold component on which wall portions of the cavities C1,C2 are integrally formed. In a subsequent step, the resultant componentmust undergo cutting for later attachment thereof through fitting as achase which partially constitutes the molding apparatus 61.

Next, the operation of the molding apparatus 61 having theabove-mentioned configuration will be described.

FIG. 7 is a graph showing characteristics of a molding apparatus in thefirst embodiment of the present invention. In FIG. 7, time is plottedalong the horizontal axis, and the temperature of the molding apparatus61 is plotted along the vertical axis.

In FIG. 7, line L1 indicates the temperature of the movable mold 13 informing a light guide plate by use of the conventional molding apparatus11; line L2 indicates the temperature of the transfer plate 34 informing a light guide plate by use of the conventional molding apparatus11; line L3 indicates the temperature of the movable mold 24B in forminga light guide plate by use of the molding apparatus 61 of the presentinvention; and line L4 indicates the temperature of the transfer plate34 in forming a light guide plate by use of the molding apparatus 61 ofthe present invention.

According to the present embodiment, in molding a light guide plate byuse of the molding apparatus 61, the temperature of the movable mold 24Bat the time of start of molding is set about 40° C. lower than that ofthe movable mold 13 at the time of start of molding of a light guideplate by use of the conventional molding apparatus 11. The temperatureof the movable mold 24B is 50° C. or more lower than the glasstransition temperature of the resin 30 to be subjected to molding. Inthis case, the temperature of the molten resin 30 is 290° C.

First, in the conventional molding apparatus 11, when the resin 30 ischarged into the cavities C1, C2 of the molding apparatus 11, thetemperatures of the movable mold 13 and the transfer plate 34 risesharply, since the temperature of the resin 30 is 290° C. However, sincethe movable mold 13 removes a lot of heat, temperature T1 of thetransfer plate 34 at time (timing) tp1 when transfer is completed isabout 120° C.

At this time, temperature T2 of the movable mold 13 is slightly inexcess of 130° C.

Therefore, the resin 30 is cooled sharply from a temperature of 290° C.by time tp1 when transfer is completed. Thus, a skin layer is apt to beformed, and a formed skin layer is apt to grow.

Meanwhile, in the conventional molding apparatus 11, pits andprojections each having a submicron size are formed on a light guideplate. The pits and projections must be formed such that the depth ofthe pits is about half the size of an opening thereof. The depth is verysmall as compared with the thickness of a skin layer.

Accordingly, in forming a light guide plate by use of the conventionalmolding apparatus 11, the resin 30 which has shifted to a solidifiedstate is crushed and plastically deformed through application of a largemold-clamping force by a mold-clamping apparatus, so as to cause theresin 30 to follow the pits and projections on the transfer plate 34. Asa result, a pattern on the transfer surface of the transfer plate 34 isapt to deteriorate.

Transfer is completed after elapse of about 1.2 second; i.e., at timetp1. Subsequently, the temperatures of the transfer plate 34 and themovable mold 13 lower gradually along substantially parallel, respectivelowering curves. Since the temperature of the molding apparatus 11 isset rather high, the temperature lowers very slowly. Thus, a time of 12seconds or more has elapsed until time tp2 when mold-opening isperformed; a time of near 16 seconds has elapsed until time tp3 when alight guide plate is ejected; and, eventually, a time of 17.2 seconds ormore has elapsed until time tp4 when mold closing of the moldingapparatus 11 is performed, whereby the next cycle of molding becomesready to start.

By contrast, in the molding apparatus 61 of the present invention, eventhough the temperature of the molding apparatus 61 at the time of startof molding is set near 40° C. lower than that of the conventionalmolding apparatus 11, the presence of the thermal insulation layer 40restricts dissipation of thermal energy of the resin 30 toward themovable mold 24B. Thus, at transfer completion time t1 (≅tp1), thetemperature of the transfer plate 34 is raised to about the same level(about 120° C.) as that of the conventional molding apparatus 11. Thetemperature rise of the transfer plate 34 is slightly gentler than thatof the transfer plate 34 used in the conventional molding apparatus 11.However, the temperature of the movable mold 24B rises to near 160° C.at a stretch.

As in the case of use of the conventional molding apparatus 11, transferis completed after elapse of about 1.2 second; i.e., at time t1 (≅tp1).However, in the case of use of the molding apparatus 61 of the presentinvention, at the initial stage of charge before completion of transfer,the resin 30 is maintained rather high in temperature and thus maintainsits fluidity. Thus, as compared with the case of use of the conventionalmolding apparatus 11, the growth of a skin layer is restricted, and thedegree of solidification is lowered. As a result, the resin 30 canreadily follow pits and projections on the transfer surface of thetransfer plate 34.

Therefore, in the present embodiment, a mold-clamping force forplastically deforming resin in the vicinity of the transfer surface;i.e., a skin layer, can be reduced. Thus, not only can the overall sizeof the injection molding machine including the mold-clamping apparatusbe reduced, but also costs can be reduced. Also, the accuracy oftransfer from the transfer surface of the transfer plate 34 can beenhanced. When a mold-clamping force equivalent to that generated in useof the conventional molding apparatus 11 is generated, the accuracy oftransfer from the transfer surface of the transfer plate 34 can beenhanced.

After completion of transfer, the temperatures of the transfer plate 34and the movable mold 24B lower. Since the temperature of the moldingapparatus 61 is set rather low, the temperatures of the transfer plate34 and the movable mold 24B decrease more quickly.

Thus, only a time of about 6.4 seconds elapses until time t2 whenmold-opening is performed; only a time of about 9.2 seconds elapsesuntil time t3 when a light guide plate is ejected; and, eventually, onlya time of about 9.6 seconds to 11.6 seconds elapses until time t4 whenmold closing is performed, whereby the next cycle of molding becomesready to start. The temperature of the transfer plate 34 at time t2 whenmold opening is performed is 34° C. lower than that of the transferplate 34, at time tp2, used in the conventional molding apparatus 11.

As mentioned above, in the present embodiment, the thermal insulationlayer 40 is disposed between the movable mold 24B and the transfer plate34, thereby restricting dissipation of thermal energy of the resin 30toward the movable mold 24B. This can restrict the formation of a skinlayer, which could otherwise result from a sharp drop in temperature ofthe resin 30. As a result, transfer accuracy can be enhanced.

Since a mold-clamping force for plastically deforming a skin layer canbe reduced, not only can the size of the injection molding machine bereduced, but also the durability of the transfer plate 34 can beenhanced.

Since the temperature of the molding apparatus 61 can be set low to anextent corresponding to the enhancement of transfer accuracy, the speedsat which the temperatures of the transfer plate 34 and the movable mold24B drop can be increased. Therefore, a molding cycle can besufficiently shortened.

Next, a second embodiment of the present invention for forming a disksubstrate will be described. Like structural elements of the first andsecond embodiments are denoted by like reference numerals. For theeffects that the second embodiment yields through employment ofstructural elements similar to those of the first embodiment, theeffects that the first embodiment yields are applied accordingly.

FIG. 8 is a pair of sectional views showing a resin molding method inthe second embodiment of the present invention, wherein (a) is a viewshowing a state in which the resin 30, which serves as a moldingmaterial, is charged into a cavity C, and (b) is a view showing a statein which mold clamping has been performed.

In FIG. 8, reference numeral 20 denotes a molding apparatus, whichserves as a resin molding apparatus for molding an article such as adisk substrate; reference numeral 24A denotes a stationary mold(stationary lower mold), which serves as a first mold member and as afirst mold; and reference numeral 24B denotes a movable mold (movableupper mold), which serves as a second mold member and as a second mold,disposed in a manner capable of advancing and retreating in relation tothe stationary mold 24A. By means of an unillustrated mold-clampingapparatus (press mechanism), the movable mold 24B is advanced; i.e.,mold closing is performed; the movable mold 24B is brought into contactwith the stationary mold 24A; i.e., mold clamping is performed, therebyforming the cavity C having a circular shape between the stationary mold24A and the movable mold 24B; and the movable mold 24B is retreated fromthe stationary mold 24A; i.e., mold opening is performed.

Reference numeral 15 denotes a sprue formed in the stationary mold 24A.Communication is established between the tip end of the sprue 15 and thecavity C. Reference numeral 62 denotes a cut punch disposed in a mannercapable of advancing and retreating in relation to the movable mold 24B.The advancing cut punch 62 can cut a hole in the resin 30 charged intothe cavity C.

As in the case of the first embodiment, the thermal insulation layer 40having a honeycomb structure is formed on a surface of the stationarymold 24A which is located within the cavity C and faces the movable mold24B. The transfer plate 34 is attached to a surface of the thermalinsulation layer 40 which faces the movable mold 24B. In the presentembodiment, a stamper is used as the transfer plate 34. The transferplate 34 has a transfer surface which faces the movable mold 24B and onwhich fine pits and projections are formed in a predetermined pattern.

The temperature-regulating channels 23 are formed in the stationary mold24A and the movable mold 24B. A temperature-regulating medium; forexample, water, is run through the temperature-regulating channels 23 soas to cool the molding apparatus 20 and the resin 30 within the cavityC.

The resin 30 in the cavity C is cooled, by the above-mentioned water, toset. At this time, the pattern on the transfer surface of the transferplate 34 is transferred onto the resin 30. Subsequently, the cut punch62 is advanced so as to cut a hole. Then, mold opening is performed,thereby yielding a disk substrate.

In the present embodiment, a disk substrate is formed. Thus, the resincharged into the cavity C is spread into the form of a thin disksubstrate. Accordingly, after transfer, the molding apparatus 20 whosetemperature is set low rapidly removes thermal energy from the resin, sothat the disk substrate can be cooled favorably. As a result, a moldingcycle can be shortened.

Notably, by means of slightly lowering the thermal insulation effect ofthe thermal insulation layer 40 and slightly increasing the temperatureof the molding apparatus 20 at the time of start of molding,intermediate characteristics can be imparted to the transfer plate 34and the movable mold 24B.

Next, the operation of the molding apparatus 20 having theabove-mentioned configuration will be described.

FIG. 9 is a graph showing characteristics of a molding apparatus in thesecond embodiment of the present invention. In FIG. 9, time is plottedalong the horizontal axis, and the temperature of the molding apparatus20 is plotted along the vertical axis.

In FIG. 9, line L1 indicates the temperature of a movable mold informing a disk substrate by use of a conventional molding apparatus formolding a disk; line L2 indicates the temperature of a transfer plate(stamper) in forming a disk substrate by use of the conventional moldingapparatus for molding a disk; line L3 indicates the temperature of themovable mold 24B in forming a disk substrate by use of the moldingapparatus 20 of the present invention; and line L4 indicates thetemperature of the transfer plate 34 in forming a disk substrate by useof the molding apparatus 20 of the present invention.

According to the present embodiment, in molding a disk substrate by useof the molding apparatus 20, the temperature of the movable mold 24B atthe time of start of molding is set about 40° C. lower than that of themovable mold at the time of start of molding of a disk substrate by useof the conventional molding apparatus for molding a disk. Thetemperature of the movable mold 24B is 50° C. or more lower than theglass transition temperature of the resin 30 to be subjected to molding.In this case, the temperature of the molten resin 30 is 290° C.

First, in the conventional molding apparatus for molding a disk, whenthe resin is charged into the cavity of the molding apparatus, thetemperatures of the movable mold and the transfer plate rise sharply,since the temperature of the resin is 290° C. However, since the movablemold removes a lot of heat, temperature T1 of the transfer plate at time(timing) tp1 when transfer is completed is about 120° C.

At this time, temperature T2 of the movable mold is slightly in excessof 130° C.

Therefore, the resin is cooled sharply from a temperature of 290° C. bytime tp1 when transfer is completed. Thus, a skin layer is apt to beformed, and a formed skin layer is apt to grow.

Meanwhile, in the conventional molding apparatus for molding a disk,pits and projections each having a submicron size are formed on a disksubstrate. The pits and projections must be formed such that the depthof the pits is about half the size of an opening thereof. The depth isvery small as compared with the thickness of a skin layer.

Accordingly, in forming a disk substrate by use of the conventionalmolding apparatus for molding a disk, the resin which has shifted to asolidified state is crushed and plastically deformed through applicationof a large mold-clamping force by a mold-clamping apparatus, so as tocause the resin to follow the pits and projections on the transferplate. As a result, a pattern on the transfer surface of the transferplate is apt to deteriorate.

Transfer is completed after elapse of about 0.3 second; i.e., at timetp1. Subsequently, the temperatures of the transfer plate and themovable mold lower gradually along substantially parallel, respectivelowering curves. Since the temperature of the conventional moldingapparatus is set rather high, the temperature lowers very slowly. Thus,a time of 3 seconds or more has elapsed until time tp2 when mold-openingis performed; a time of near 4 seconds has elapsed until time tp3 when adisk substrate is ejected; and, eventually, a time of 4.3 seconds ormore has elapsed until time tp4 when mold closing of the conventionalmolding apparatus for molding a disk is performed, whereby the nextcycle of molding becomes ready to start.

By contrast, in the molding apparatus 20 of the present invention, eventhough the temperature of the molding apparatus 20 at the time of startof molding is set near 40° C. lower than that of the conventionalmolding apparatus for molding a disk, the presence of the thermalinsulation layer 40 restricts dissipation of thermal energy of the resin30 toward the stationary mold 24A. Thus, at transfer completion time t1(≅tp1), the temperature of the transfer plate 34 is raised to about thesame level (about 120° C.) as that of the conventional molding apparatusfor molding a disk. The temperature rise of the transfer plate 34 isslightly gentler than that of the transfer plate 34 used in theconventional molding apparatus for molding a disk. However, thetemperature of the movable mold 24B rises to near 160° C. at a stretch.

As in the case of use of the conventional molding apparatus for moldinga disk, transfer is completed after elapse of about 0.3 second; i.e., attime t1 (≅tp1). However, in the case of use of the molding apparatus 20of the present invention, at the initial stage of charge beforecompletion of transfer, the resin 30 is maintained rather high intemperature and thus maintains its fluidity. Thus, as compared with thecase of use of the conventional molding apparatus for molding a disk,the growth of a skin layer is restricted, and the degree ofsolidification is lowered. As a result, the resin 30 can readily followpits and projections on the transfer surface of the transfer plate 34.

Therefore, in the present embodiment, a mold-clamping force forplastically deforming resin in the vicinity of the transfer surface;i.e., a skin layer, can be reduced. Thus, not only can the overall sizeof the injection molding machine including the mold-clamping apparatusbe reduced, but also costs can be reduced. Also, the accuracy oftransfer from the transfer surface of the transfer plate 34 can beenhanced. When a mold-clamping force equivalent to that generated in useof the conventional molding apparatus for molding a disk is generated,the accuracy of transfer from the transfer surface of the transfer plate34 can be enhanced.

After completion of transfer, the temperatures of the transfer plate 34and the movable mold 24B lower. Since the temperature of the moldingapparatus 20 is set rather low, the temperatures of the transfer plate34 and the movable mold 24B decrease more quickly.

Thus, only a time of about 1.6 second elapses until time t2 whenmold-opening is performed; only a time of about 2.3 seconds elapsesuntil time t3 when a disk substrate is ejected; and, eventually, only atime of about 2.4 seconds to 2.9 seconds elapses until time t4 when moldclosing is performed, whereby the next cycle of molding becomes ready tostart. The temperature of the transfer plate 34 at time t2 when moldopening is performed is 34° C. lower than that of the transfer plate 34,at time tp2, used in the conventional molding apparatus for molding adisk.

As mentioned above, in the present embodiment, the thermal insulationlayer 40 is disposed between the stationary mold 24A and the transferplate 34, thereby restricting dissipation of thermal energy of the resin30 toward the movable mold 24B. This can restrict the formation of askin layer, which could otherwise result from a sharp drop intemperature of the resin 30. As a result, transfer accuracy can beenhanced.

Since a mold-clamping force for plastically deforming a skin layer canbe reduced, not only can the size of the injection molding machine bereduced, but also the durability of the transfer plate 34 can beenhanced.

Since the temperature of the molding apparatus 20 can be set low to anextent corresponding to the enhancement of transfer accuracy, the speedsat which the temperatures of the transfer plate 34 and the movable mold24B drop can be increased. Therefore, a molding cycle can besufficiently shortened.

In the first and second embodiments, the honeycomb structure is formedon the transfer plate 34 or on either the stationary mold 24A or themovable mold 24B. However, the honeycomb structure can be formed byother methods.

A third embodiment of the present invention in which the honeycombstructure is formed by another method will next be described.

FIG. 10 is a first view showing a method for forming a thermalinsulation layer in the third embodiment of the present invention. FIG.11 is a second view showing the method for forming a thermal insulationlayer in the third embodiment of the present invention.

For example, in metal injection molding, difficulty may be encounteredin charging a green substance which contains metal powder, into deepgrooves each having a width of about 10 μm. In such a case, for example,as shown in FIGS. 10 and 11, a thin plate 70 which contains metal powderis prepared beforehand by metal injection molding. A negative-honeycombtransfer plate 72 (used to form the thermal insulation layer 40) havinga negative honeycomb structure (a structure having acicular protrusions)is pressed against the thin plate 70. In this state, the thin plate 70and the negative-honeycomb transfer plate 72 are pressed against eachother under pressure generated by an unillustrated press, whereby thenegative honeycomb structure is transferred onto the thin plate 70.Subsequently, the negative-honeycomb transfer plate 72 is separated fromthe thin plate 70, thereby yielding a thin plate 70A, which is anegative structure having a transferred honeycomb structure as shown inFIG. 11. The thin plate 70A can be disposed as a thermal insulationlayer between the transfer plate 34 and either the stationary mold 24Aor the movable mold 24B.

Next, a fourth embodiment of the present invention in which a honeycombstructure is formed by still another method will be described.

FIG. 12 is a pair of views showing a method for forming a thermalinsulation layer in the fourth embodiment of the present invention,wherein (a) is a view showing a state before transfer of a honeycombstructure, and (b) is a view showing a state after transfer of thehoneycomb structure.

This method uses an amorphous metal (so-called “metal glass”) havinghigh fluidity and wear resistance. As shown in FIG. 12( a), an amorphousmetal 86 is placed on a mold mirror plate 84 which is heated in a sleeve82 by use of a heating coil 80, which serves as a heating element.Press-forming is performed in such a manner that a negative-honeycombtransfer plate 88 (used to form a thermal insulation layer) having anegative honeycomb structure is pressed against the amorphous metal 86as shown in FIG. 12( b), whereby the negative honeycomb structure can betransferred onto the amorphous metal 86. Subsequently, thenegative-honeycomb transfer plate 88 is separated from the amorphousmetal 86, thereby yielding an amorphous metal layer 86A, which is anegative structure having a transferred honeycomb structure. The moldmirror plate 84 on which the amorphous metal layer 86A is formed as athermal insulation layer can be used as a chase which partiallyconstitutes the molding apparatus 20, and be disposed between thetransfer plate 34 and either the stationary mold 24A or the movable mold24B.

The present invention is not limited to the above-described embodiments.Numerous modifications and variations of the present invention arepossible in light of the spirit of the present invention, and they arenot excluded from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a molding apparatus of aninjection molding machine.

1. A resin molding apparatus comprising: (a) a first mold; (b) a secondmold disposed in opposition to the first mold; (c) a transfer plateattached to one of the first and second molds and comprising a transfersurface bearing a pattern of pits and projections and oriented toward acavity; and (d) a thermal insulation layer disposed between the transferplate and the one of the first and second molds and formed throughgrowth from the transfer plate side or from the one of the first andsecond mold sides.
 2. A resin molding apparatus according to claim 1,wherein the thermal insulation layer is formed through growth from thetransfer plate side.
 3. A resin molding apparatus according to claim 1,wherein the thermal insulation layer is formed through growth from theone of the first and second molds.
 4. A resin molding apparatusaccording to claim 1, wherein: (a) the thermal insulation layercomprises a honeycomb structure, and (b) a honeycomb pitch of thehoneycomb structure is 0.1 μm to 100 μm inclusive.
 5. A resin moldingapparatus according to claim 1, wherein: (a) the thermal insulationlayer comprises a honeycomb structure, and (b) a wall thickness of thehoneycomb structure is 0.01 μm to 10 μm inclusive.
 6. A resin moldingapparatus according to claim 1, wherein: (a) the thermal insulationlayer comprises a honeycomb structure, and (b) a honeycomb height of thehoneycomb structure is 10 μm to 10 mm inclusive.
 7. A resin moldingapparatus according to claim 4, wherein the thermal insulation layercomprises a stack of honeycomb structures.
 8. A resin molding apparatusaccording to claim 1, wherein the temperature of the one of the firstand second molds as measured when molding is started is set 50° C. ormore lower than a glass transition temperature of a molding material. 9.A resin molding method of a resin molding apparatus comprising a firstmold, a second mold disposed in opposition to the first mold, a transferplate attached to one of the first and second molds and comprising atransfer surface bearing a pattern of pits and projections and orientedtoward a cavity, and a thermal insulation layer disposed between thetransfer plate and the one of the first and second molds and formedthrough growth from the transfer plate side or from the one of the firstand second mold sides, comprising: (a) charging a molding material intothe cavity and transferring the pattern onto the molding material, and(b) after transfer of the pattern, applying a mold-clamping force so asto plastically deform a portion of the molding material in the vicinityof the transfer surface.